The present invention relates to a through-flow steam generator with feed water pump, economizer, evaporator and water separator, which are connected in series, as well as a circulating pipe with a circulating pump connected to the water outlet of the water separator. The economizer is on a higher level than the evaporator entry. A method for operating the arrangement is also disclosed.
Vapor is formed in the economizer after shutdown of such a steam generator. If the steam generator now has to be filled, then this can only take place by way of small feed charges because otherwise a too rapid temperature drop occurs. This leads to unacceptable thermal stresses in the structural parts. On the other hand, in order to carry along the steam bubbles, which are formed, it is necessary to have feed water quantities as large as possible.
In a known forced flow-through steam generator of the type mentioned initially (German Patent DE-B No. 2740883) a charge pipe with a valve is branched off between the feed water pump and a downstream closure valve. This by-passes the economizer and leads to the evaporator entry. The economizer has means for aeration at the level of its highest geodesical height. This forced flow-through steam generator is put into operation thereby the evaporator and the separator are charged with feedwater through the charging pipe and that thereafter, with evaporated economizer, water is re-pumped from the evaporator via the separator. The steam generator is subsequently fired and the economizer is charged in reverse through the charging pipe with water in saturated condition from the evaporator. In this manner, as a result of spontaneous condensation on feeding into the economizer, hammer is to be avoided. This arrangement has the disadvantage that high control expenditure is necessary, that the circulation pump has to be in operation continuously, and that pressure increases have to be limited.
According to another known steam generator (German Patent DE-A No. 28 40 603), in order to avoid evaporation in the economizer during starting, a control valve is placed between the economizer and the evaporator, upstream of which a water discharge pipe branches off as bypass to the evaporator. By partially closing the control valve, the water pressure in the economizer is temporarily increased to such an extent that evaporation does not occur. This arrangement requires, in addition to an increased expenditure in control, a separate safety arrangement in order to prevent excess pressure in the economizer. In addition, the pressure valves are subjected to wear, and represent therewith an additional source of breakdown.